Field of the Invention
The present disclosure relates to an image reading apparatus that irradiates light on an original document and reads an image, and an image forming apparatus including the image reading apparatus.
Description of the Related Art
A configuration of an image reading apparatus that illuminates an original document is known, in which the image reading apparatus includes a circuit board that includes a plurality of light emitting elements, and a light guide that guides light, towards the original document, that has been output from the light emitting elements. When the light emitting elements are turned on for reading an image, the temperatures of the light emitting elements increase. When the temperatures of the light emitting elements increase, the temperature of the circuit board including the light emitting elements, and the temperature of the light guide disposed in the vicinity of the light emitting elements increases as well. The circuit board and the light guide are formed of different materials, and the linear expansion coefficient of the circuit board and that of the light guide differ. Accordingly, the amount of expansion of the circuit board and that of the light guide differ during increase in temperature such that the light guide, disadvantageously, becomes warped with respect to the circuit board. When the light guide becomes warped with respect to the circuit board, the positional relationship between the light emitting elements and the light guide becomes out of alignment and, as a result, may lead to decrease in light efficiency and change in the illuminance distribution.
The following technique is known that overcomes the above problem. A circuit board is configured as a planar member formed of metal, and surfaces of a light guide and the circuit board facing each other include an adhesive member such that heat of the light emitting elements is diffused by the planar member formed of metal. Warping of the light guide is suppressed in the above manner (Japanese Patent Laid-Open No. 2013-223186).